The nominal operating supply voltage for semiconductor integrated circuits is falling steadily because of the need to reduce power consumption and maintain high reliability. Furthermore, the advent of System on Chip (SOC) technology and Application-Specific Integrated Circuits (ASIC) increases the tendency to integrate different core subsystems at different supply voltages into the same semiconductor integrated circuit. High voltage output drivers are needed to interface between the core subsystems of different supply voltages. Conventional high voltage output drivers usually include a voltage level shifter stage and an output stage. The voltage level shifter stage generates the pull-up and pull-down signal to convert the low voltage input signal to a high voltage output signal. The input circuit of the voltage level shifter stage is typically operational at a low voltage level and thus is fabricated using the 0.35 μm process. The output stage receives the output signal at a higher voltage level (i.e., 3.3 volts) and thus is fabricated using the 0.8 μm process. As such, a dual oxide process is necessary to provide an input circuit using 0.35 μm technology and an output circuit using 0.8 μm technology. Utilizing such a dual process is expensive and produces slow switching speeds. Moreover, as the devices continue to shrink in size and increase in speed, high voltage output drivers with dual gate oxide components are no longer suitable for many applications.
Some prior art high voltage output drivers use high voltage cascode devices to solve the above identified problems. However, these high voltage output drivers are not fast enough for many applications. In addition, they exhibit DC leakage current problems, high power consumption, high internal voltage swing problems, and slow switching speed.
Thus, there is a need in the art for a high speed output driver that does not require dual gate processes. In addition, there is a need for a high speed output driver having high switching speed, low power consumption, low leakage current, and minimal output waveform distortion. The present invention meets the above needs.